Downhole apparatus and method

ABSTRACT

There is provided a method of stabilising at least a portion of downhole toolstring, and associated apparatus. The method comprises stabilising the portion of downhole toolstring whilst an apparatus and/or the portion of downhole toolstring is/are in and/or passing through a soft formation with hard inclusions. The method comprises reaming the hard inclusions with a reaming portion ( 11 ) of a downhole apparatus whilst a stabilising portion ( 1 ) of the downhole apparatus stabilises the reaming portion ( 11 ) and/or the portion of downhole toolstring.

TECHNICAL FIELD

The present invention relates to downhole apparatus and methods. More particularly, but not exclusively, embodiments of the invention relate to methods and associated downhole apparatus for stabilising a toolstring in a borehole, such as stabilising a drill string in a borehole in at least a soft portion of formation.

BACKGROUND

Within the oil and gas industry the use of horizontal and extended reach oil and gas wells is becoming common practice but the increased use of this methodology brings with it significant challenges. For example, the present Applicant has identified that there is significant wear experienced in drilling assembly components such as drill pipe, drill collars and stabilisers when drilling very high angle bore hole. The present Applicant believes that this problem may become particularly problematic in formations containing chert nodules, conglomerates and boulder type materials in other wise relatively soft formations.

The present Applicant has deduced that these types of formation tend to deflect the path of the drill bit causing the bore hole to change direction over very small distances as the drill bit is deflected into the softer formation rather than drilling through the chert nodules, large pieces of conglomerate or boulder material, resulting in projections or ledges being formed in the bore hole wall.

The present Applicant has deduced that stabilisers following this deflected borehole path now have a tendency to catch up on these ledges or projections resulting in damage to the leading edge of the stabiliser upset section which in turn leads to the early failure of the gauge protection on the hard faced crown length of the stabiliser and consequent loss of gauge.

The present Applicant believes that severe step changes dog legs and other detrimental changes in bore hole geometry in hard formations can be sought to be addressed by the use of various types of existing reamer tools such as roller reamers and the like. However the present Applicant believes that in relatively soft formations containing medium to large mass objects of harder rock such as chert nodules conglomerate or boulder type materials, the use of conventional reaming techniques would not provide a satisfactory solution; especially in long sections of high angle or horizontal borehole. The present Applicant has identified that borehole which has been deflected by medium to large mass objects of hard rock is very difficult to rectify after the event has occurred because any reaming tool run after the event will tend to ride over or deflect past the projecting mass further enlarging the borehole section to allow the reamer assembly past. This will provide a partial solution but will lead to severe vibration and potential wear problems when stabilised drilling tools or assemblies are rotated through this section in future drilling operations.

The present Applicant believes that in vertical and low angle borehole this situation may not be such a major issue; but in high angle and horizontal borehole it will be. The present Applicant believes that, for example, if long sections of borehole suffer from this problem then it will lead to poor rates of drill bit penetration due to hang up on the stabilisation and other components in the drilling assembly. The present Applicant believes that it will also lead to severe vibration and consequent damage of drilling assembly components such as the rotary steerable system and its associated onboard electronics as well as damage to the PDC cutting structure of the drill bit shortening the drill bit run life.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method of stabilising at least a portion of downhole toolstring. The method may comprise stabilising the portion of downhole toolstring whilst an apparatus and/or the portion of downhole toolstring is/are in and/or passing through a soft formation. The soft formation may comprise a relatively soft formation, such as in comparison to hard inclusions in the soft formation, such as boulder type materials, conglomerates, cherts or other nodules, or the like, The method may comprise stabilising the portion of downhole toolstring whilst the apparatus and/or the portion of downhole toolstring are in and/or passing through a soft formation with hard inclusions. The method may comprise reaming the hard inclusions. The method may comprise reaming the hard inclusions with a reaming portion of a downhole apparatus whilst a stabilising portion of the downhole apparatus stabilises the reaming portion and/or the portion of downhole toolstring.

The method may comprise a stabilised method of reaming. The method may comprise reducing, minimising and/or preventing deflection or deviation of a borehole, such as deflection or deviation attributable to a hard inclusion in a relatively soft formation. The method may comprise reaming hard inclusions projecting into the borehole or into the intended path of the borehole, such as hard inclusions around which a drill bit and/or BHA may have at least partially deflected. The method may comprise substantially only reaming hard inclusions in a soft formation. The method may comprise only reaming hard inclusions in a soft formation. The method may comprise stabilising the portion of toolstring against a borewall/s of soft formation. The method may comprise substantially not reaming the soft formation. The method may comprise stabilising and/or reaming at or to a gauge or diameter substantially similar to the gauge of pre-drilled borehole. The method may comprise stabilising and/or reaming at or to a gauge or diameter substantially similar to and just less than the gauge of pre-drilled borehole. For example, the method may comprise stabilising at a maximum diameter 0.020″ to 0.030″ below borehole diameter. The method may comprise stabilising with a stabilising portion with a major crown length diameter of 0.020″ to 0.030″ below borehole diameter. The method may comprise stabilising with a fixed stabilising portion. For example, the method may comprise stabilising with a stabilising portion without a possibility of relatively moving parts, such as for extension, expansion or retraction of the stabilising portion.

The method may comprise reaming of hard inclusions with a reaming portion extending up to almost full gauge diameter. The method may comprise reaming of hard inclusions with a reaming portion extending up to almost full gauge diameter of the apparatus. The method may comprise reaming with a reaming portion that terminates just before the major diameter crown length of the stabilising portion of the apparatus.

The method may comprise reaming with a reaming portion extending from a lesser outer reaming diameter up to maximum outer reaming diameter. The maximum outer reaming diameter may be less than the full gauge diameter of the borehole. The maximum outer reaming diameter may be less than the full gauge diameter of the apparatus. The lesser outer reaming diameter may correspond to a lesser outer diameter of the toolstring, such as an outer diameter of a tubular or drill collar or the like.

The method may comprise reaming with a reaming portion extending along a leading axial portion of an upset portion of an apparatus. The method may comprise reaming with a reaming portion that extends or projects outwards from the lesser outer diameter of the toolstring, such as the outer diameter of the tubular or drill collar or the like. The method may comprise reaming with an angled reaming portion extending axially backwards and radially outwards along the leading axial portion of an upset portion. The method may comprise reaming with a reaming portion with a shallow lead angle up to the crown of the upset portion.

The method may comprise initially reaming with a part or surface of the reaming portion at or close to the diameter of the toolstring, such as of similar minimal diameter to a drill collar, tubular or the like. Initially reaming at or close to the diameter of the toolstring may allow reaming and movement of the apparatus in an axial (e.g. downhole) direction when a hard inclusion is encountered. For example, rather than reaming a soft portion diametrically opposite the hard inclusion, such as may be initiated by a conventional reamer, the present invention stabilises or bears against the soft formation diametrically opposite the hard inclusion, without reaming said soft formation diametrically opposite the hard inclusion.

The apparatus may be supported proximal the reaming portion, such as stabilised in the borehole by the stabilising portion.

The method may comprise stabilising the apparatus. For example, the method may comprise reaming with a reaming portion directly adjacent the stabilising portion for stabilising. The method may comprise stabilising the apparatus/toolstring directly behind the reaming portion, behind being taken in the direction of transit of the apparatus/toolstring. The method may comprise stabilising the toolstring/apparatus uphole and/or downhole of the reaming portion. The method may comprise initially reaming with a part or surface of the reaming portion at or close to the diameter of the toolstring, such as of similar minimal diameter to a drill collar, tubular or the like. Initially reaming at or close to the diameter of the toolstring may allow reaming and movement of the apparatus in an axial (e.g. downhole) direction when a hard inclusion is encountered. For example, rather than reaming a soft portion diametrically opposite the hard inclusion, such as may be initiated by a conventional reamer, the present invention continues in a path aligned with the borehole at least during initial reaming of the hard inclusion; and optionally continues in the path aligned with the borehole at least during reaming up to the maximum diameter of the reaming portion.

The method may comprise stabilising the toolstring/apparatus adjacent the reaming portion such that the reaming portion is substantially prevented from deviating or deflecting from a path aligned with the borehole. The method may comprise stabilising the toolstring/apparatus adjacent the reaming portion with a stabilising portion of larger diameter than the reaming portion. The larger diameter stabilising portion may comprise a non-aggressive bearing outer surface such that the stabilising portion bears on the formation rather than reaming or eroding the formation.

The method may comprise reaming with a reaming portion of lesser diameter in advance of stabilising with a stabilising portion of greater diameter. The method may comprise reaming with the reaming portion of lesser diameter in advance of stabilising with the stabilising portion of greater diameter as the apparatus/toolstring transits downhole, such as during drilling with a drillstring. In addition, or alternatively, the method may comprise reaming with the reaming portion of lesser diameter in advance of stabilising with the stabilising portion of greater diameter as the apparatus/toolstring transits uphole, such as during retrieval or pulling of a drillstring. Accordingly, the method may comprise stabilising with a stabilising portion sandwiched between or flanked by two reaming portions. The stabilising portion may be directly sandwiched or flanked by the two reaming portions.

According to a further aspect of the present invention there is provided a downhole apparatus for stabilising at least a portion of downhole toolstring in a borehole.

The apparatus may be configured to stabilise the portion of downhole toolstring whilst the apparatus and/or the portion of downhole toolstring are in and/or passing through a soft formation.

The apparatus may comprise a fixed apparatus. The apparatus may comprise a fixed diameter or fixed gauge apparatus. The apparatus may comprise a stabiliser. The stabiliser may comprise a fixed stabiliser. The stabiliser may comprise a fixed blade stabiliser. The fixed apparatus may be moveable with the toolstring, such as up and/or downhole and by rotation, such as by a rotary table or downhole motor or the like.

The apparatus may comprise a throughbore, such as for the passage of fluid therethrough. The throughbore may be for the passage of drilling fluid, wellbore fluid, injection fluid or the like. The apparatus may comprise upper and/or lower connections, such as threaded box connections, for connection to upper and lower portions of toolstring, such as tubulars, drill collars, or the like. The apparatus may comprise upper and/or lower body portion, such as body portion/s of similar outer diameter to the upper and/or lower portions of toolstring.

The apparatus may be configured to stabilise the portion of downhole toolstring whilst the apparatus and/or the portion of downhole toolstring is/are in and/or passing through a soft formation. The apparatus may be configured to stabilise the portion of downhole toolstring whilst the apparatus and/or the portion of downhole toolstring is/are in and/or passing through a soft formation with hard inclusions, such as chert, conglomerates, nodules or the like. The apparatus may be configured to stabilise in soft formation and ream hard inclusions, such as ledges or mass projections into the borehole.

The apparatus may comprise one or more upset portion/s extending radially from a lesser outer diameter of the apparatus to a maximum outer diameter of the apparatus.

The one or more upset portion/s may comprise a reaming portion/s and/or a stabilising portion/s.

A single upset portion may comprise the reaming portion/s and the stabilising portion/s. For example, the single upset portion may comprise two reaming portions (e.g. for downhole and uphole reaming) and a single stabilising portion positioned or sandwiched between the two reaming portions.

Alternatively, a plurality of upset portions may comprise the reaming portion/s and the stabilising portion/s. For example, a first upset portion may comprise a downhole reaming portion for reaming in a downhole direction; and a second upset portion may comprise the stabilising portion. Optionally the apparatus may comprise a third upset portion comprising an uphole reaming portion for reaming in an uphole direction. Alternatively optionally, the second upset portion may comprise the stabilising portion and one of the reaming portions, such as the uphole reaming portion.

The plurality of upset portions may be closely coupled. The plurality of upset portions may be provided by or on a plurality of tools, such as a plurality of subs that may be (directly) connected together. The plurality of upset portions may be provided in a piggy back or sleeve type arrangement.

The apparatus may comprise a maximum outer diameter for stabilising and/or reaming at or to a gauge or diameter substantially similar to the gauge of pre-drilled borehole. The upset portion/s may be configured to stabilise and/or ream at or to a gauge or diameter substantially similar to and just less than the gauge of pre-drilled borehole. For example, the stabilising portion/s may comprise a maximum diameter 0.020″ to 0.030″ below borehole diameter. The reaming portion may be provided along an axial length of the apparatus, the axial length extending in the axial direction of the borehole. The reaming portion may be provided on a progressive angled section of the upset portion, extending rearwards and outwards from a leading or front section of the upset portion. The reaming portion may comprise an aggressive surface. The reaming portion may comprise an array of pockets formed to accommodate reaming inserts, such as diamond impregnated carbide inserts. The reaming portion may comprise diamond inserts, such as domed diamond inserts. Only the reaming portion may comprise domed diamond inserts. The diamond inserts may comprise saddle inserts.

The upset portion may comprise grooves or spiralled slots, such as to accommodate fluid and cutting debris bypass. The grooves or spiralled slots may extend axially along the upset portion, such as adjacent bearing surface/s of the stabilising portion.

The stabilising portion may comprise a non-aggressive surface, such as a non-aggressive hard facing. The stabilising portion may comprise a bearing surface/s. The stabilising portion may comprise only of bearing surface/s.

The stabilising portion may comprise carbide plaquet hard facing along the crown length of the stabilising portion.

The stabilising portion may comprise pockets for receiving inserts. For example, the stabilising portion may comprise an array of pockets for receiving stabilising diamond inserts. The stabilising diamond inserts may comprise flat or flattened diamond inserts, such as to provide flat, non-aggressive bearing surface/s. The stabilising diamond inserts may be ground or configured to define the maximum outer diameter or gauge of the stabilising portion. The stabilising diamond inserts may be ground or configured after insertion in the pockets to define the maximum outer diameter or gauge of the stabilising portion. The stabilising diamond inserts may be configured to only project minimally from the pockets. For example, the stabilising diamond inserts may be configured to project no more than 3 mm, 2 mm or 1 mm from the pockets.

The upset portion may comprise a transition portion between the reaming portion and the stabilising portion. The transition portion may be configured to protect or shield the stabilising portion. The transition portion may provide a lee or shield for the stabilising portion. The transition portion may comprise an aggressive portion. The transition portion may comprise diamond inserts, such as domed and/or saddle diamond inserts. The transition portion may comprise a steeper angle relative to at least part of the reaming portion, such as immediately prior to the transition portion. The transition portion may comprise a chamfered collar or shoulder projecting radially outwards fore of the stabilising portion.

The apparatus may be configured to substantially only ream hard inclusions in a soft formation. The apparatus may be configured to only ream hard inclusions in a soft formation. The apparatus may be configured to stabilise the portion of toolstring against a borewall/s of soft formation. The apparatus may be configured to substantially not ream the soft formation. The apparatus may be configured to not ream the soft formation. The apparatus may be configured to stabilise and/or ream at or to a gauge or diameter substantially similar to the gauge of pre-drilled borehole.

The stabilising portion may comprise a major crown length diameter substantially similar to the gauge of pre-drilled borehole. The major crown length diameter may be substantially similar to and just less than the gauge of pre-drilled borehole. The stabilising portion may comprise a major crown length diameter of 0.020″ to 0.030″ below borehole diameter. The stabilising portion may comprise a fixed stabilising portion. For example, the stabilising portion may comprise no relatively moving parts, such as for extension, expansion or retraction of the stabilising portion. The reaming portion may comprise a fixed reaming portion. For example, the reaming portion may comprise no relatively moving parts, such as for extension, expansion or retraction of the reaming portion.

The reaming portion may extend up to almost full gauge diameter. The reaming portion may extend up to almost full gauge diameter of the apparatus. The reaming portion may terminate just before the major diameter crown length of the stabilising portion of the apparatus. The reaming portion may extend from a lesser outer reaming diameter up to maximum outer reaming diameter. The maximum outer reaming diameter may be less than the full gauge diameter of the borehole. The maximum outer reaming diameter may be less than the full gauge diameter of the apparatus. The lesser outer reaming diameter may correspond to a lesser outer diameter of the toolstring, such as an outer diameter of a tubular or drill collar or the like. The reaming portion may terminate at a diameter just before the major diameter crown length of the stabilising portion of the apparatus. The maximum outer reaming diameter may be less than the maximum outer diameter of the stabilising portion of the apparatus. The apparatus may comprise no reaming portion at its maximum outer diameter or gauge. The apparatus may comprise no aggressive reaming portion or surface at its maximum outer diameter or gauge. The apparatus may comprise only non-aggressive surface/s at its maximum outer diameter or gauge.

The reaming portion may extend or run along a leading axial portion of the upset portion of the apparatus. The reaming portion may extend or project outwards from the lesser outer diameter of the toolstring, such as the outer diameter of the tubular or drill collar or the like. The reaming portion may comprise an angled reaming portion extending axially backwards and radially outwards along the leading axial portion of the upset portion. The reaming portion may comprise a shallow lead angle up to the crown of the upset portion.

The reaming portion may be directly adjacent the stabilising portion for stabilising. The stabilising portion may be directly behind the reaming portion, behind being taken in the direction of transit of the apparatus/toolstring. The apparatus may comprise a reaming portion of lesser diameter for reaming in advance of stabilising with a stabilising portion of greater diameter. The method may comprise reaming with the reaming portion of lesser diameter in advance of stabilising with the stabilising portion of greater diameter as the apparatus/toolstring transits downhole, such as during drilling with a drillstring. In addition, or alternatively, the method may comprise reaming with the reaming portion of lesser diameter in advance of stabilising with the stabilising portion of greater diameter as the apparatus/toolstring transits uphole, such as during retrieval or pulling of a drillstring. Accordingly, the method may comprise stabilising with a stabilising portion sandwiched between or flanked by two reaming portions. The stabilising portion may be directly sandwiched or flanked by the two reaming portions.

The apparatus may comprise an apparatus for directional drilling.

The apparatus may comprise a reaming stabiliser. The upset portion may be comprised in or on the reaming stabiliser. The apparatus may comprise a stabilised reamer. The upset portion may be comprised on the stabilised reamer.

The apparatus may comprise combining non-aggressive stabilisation with active aggressive diamond or diamond impregnated reaming capability in the same tool or coupled in very close proximity in order to create a stabilised method of reaming through chert nodules, conglomerates and boulder type materials in other wise relatively soft formations with minimum borehole deflection.

The apparatus may comprise a new hybrid fully stabilised diamond drilling reamer tool with unique geometry developed to provide optimum stabilisation and stabiliser life while being capable of reaming medium to large mass objects of harder rock such as chert nodules conglomerate or boulder type materials in relatively soft formations with minimum deflection or enlargement of the borehole.

According to a further aspect of the present invention there is provided a toolstring comprising at least one downhole apparatus according to any other aspect.

The toolstring may comprise a plurality of downhole apparatus according to any other aspect. The apparatus may be mounted near-bit and/or more distal to the bit. For example, the apparatus may comprise a near-bit stabiliser. In addition, or alternatively the apparatus may comprise a string stabiliser. The toolstring may comprise a Bottom Hole Assembly (BHA). The BHA may comprise the plurality of downhole apparatus. Each apparatus of the toolstring or BHA may comprise a similar apparatus. For example, each apparatus may comprise a similar gauge. Alternatively, the apparatus may be different, such as of dissimilar gauge.

The toolstring may comprise a single downhole apparatus according to any other aspect. The toolstring may comprise a BHA with the single downhole apparatus according to any other aspect.

The toolstring may comprise a drill string. The drill string may comprise a directional drill string.

The invention includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. For example, it will readily be appreciated that features recited as optional with respect to the first aspect may be additionally applicable with respect to any of the other aspects or embodiments, without the need to explicitly and unnecessarily list those various combinations and permutations here. For example, features recited with respect to an upset portion of one aspect may be applicable to the upset portion of another aspect, and vice-versa. Similarly the features recited in respect of any apparatus aspect or embodiment may be similarly applicable to a method aspect or embodiment, and vice-versa. For example, the apparatus may be configured to perform any of the functions or steps of a method aspect; and/or a method aspect may comprise any/all of the functions or steps associated with an apparatus aspect.

In addition, corresponding means for performing one or more of the discussed functions are also within the present disclosure.

It will be appreciated that one or more embodiments/aspects may be useful instabilising. In particular it will be appreciated that one or more embodiments/aspects may be useful in stabilising a toolstring in a borehole, such as stabilising a drill string in a borehole in at least a soft portion of formation.

The above summary is intended to be merely exemplary and non-limiting.

As used herein, the term “comprise” is intended to include at least: “consist of”; “consist essentially of”; “include”; and “be”. For example, it will be appreciated that where the apparatus may “comprise a stabiliser”, the apparatus may “include a stabiliser” (and optionally other element/s); the apparatus “may be a stabiliser”; or the apparatus may “consist of a stabiliser”; etc. For brevity and clarity not all of the permutations of each recitation of “comprise” have been specifically stated. Similarly, as used herein, it will be appreciated that “downhole” and “uphole” do not necessarily relate to vertical directions or arrangements, such as when applied in deviated, non-vertical or horizontal bores.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows an apparatus according to a first embodiment of the present invention, in the form of a hybrid stabiliser unit showing the combination of a diamond insert set shallow lead angle up to a crown length diameter where diamond inserts are set to cover a transition between a leading edge of a hard faced crown and a hard faced non-aggressive stabilised section of the crown length;

FIG. 2 shows a saddle style domed diamond impregnated insert;

FIG. 3 shows a hemispherical dome diamond impregnated insert;

FIG. 4 shows a semi domed diamond impregnated insert;

FIG. 5 shows an isometric view an apparatus according to an embodiment of the present invention, in the form of a hybrid stabilised drilling reamer body with no diamond inserts installed to show insert pocket position and body geometry;

FIG. 6 shows an enlarged view of FIG. 5;

FIG. 7 shows a further enlarged view of FIG. 6 with diamond impregnated inserts installed into the insert pockets and non-aggressive type hard facing applied to the crown length of the hybrid stabilised drilling reamer tool;

FIG. 8 shows a schematic sketch of a borehole section 19 passing through relatively soft formation containing medium to large mass objects such as chert nodules, conglomerate or boulder type rock material where these large mass object have caused borehole deflection;

FIG. 9 shows a schematic sketch of the same section of borehole 19 showing a hybrid stabilised diamond drilling reamer tool having reamed off one rock projection approaching the next hard rock projection; and

FIG. 10 shows a schematic view of an embodiment of the present invention in the form of a close coupled diamond impregnated fixed blade reamer connected to a conventional shortened oilfield stabiliser (Big sub or Dog sub).

DETAILED DESCRIPTION OF THE DRAWINGS

Referring first to FIG. 1 of the accompanying drawings, there is shown a downhole apparatus for stabilising at least a portion of downhole toolstring in a borehole. The apparatus is configured to stabilise the portion of downhole toolstring whilst the apparatus is in a soft formation with hard inclusions, such as chert, conglomerates, nodules or the like. The apparatus comprises a reaming portion for reaming the hard inclusions; and a stabilising portion for stabilising the reaming portion whilst reaming, as is explained in more detail below.

The embodiment shown in FIG. 1 is of a stabilised diamond drilling reamer tool which combines in one integral body the stability of a conventional drilling stabiliser technology with the reaming capability of diamond inserts which may be in the form of poly crystalline diamond compact type inserts or diamond impregnated carbide post type inserts. Due to the high probability of intermittent cutting and high impact loads together with the fact that chert and conglomerate or boulder type mass objects are extremely hard, diamond impregnated carbide post type inserts are the preferred option.

The integral non aggressive stabilised section of the body 1 will provide a stable rotating axis in line with the borehole which will not be easily deflected in softer formation, providing a stable rotating platform for the integral reaming section made up of diamond impregnated carbide inserts 12 and 13 set into the shallow lead angle up to the crown to cut away any projections of hard rock ledges within the borehole. This is in contrast to conventional roller reamers or diamond set fixed cutter reamers, which have the ability to ream on their major outer diameter: because their ability to cut on their outer diameter will cause them to cut the softer formation in preference to the hard rock projections and ledges, leading to bore hole enlargement and borehole deflection.

Now referring to FIG. 5 which shows the body 1 of the preferred embodiment prior to the installation of diamond impregnated carbide inserts and the application of carbide plaquet hard facing along the crown length. This body 1 takes the form of a drilling stabiliser with a through bore and threadable connection means 3 and 4 at each end. The upper and lower sections 2 and 2 a having a diameter compatible with the drilling tubulars onto which it is connected. The upset portion in the middle differing from a conventional drilling stabiliser in that it has a progressive angled section 5,6,7,8 leading up to the crown length diameter of the main body 1 as opposed to a shorter more steeply sloped lead from the upper and lower section diameters 2 and 2 a to the crown length on the major diameter of the upset portion of the main body 1. This progressive angled section 5,6,7 and 8 comprises an array of pockets 11 formed to accommodate diamond impregnated carbide insert 12,13 or 14. Spiralled slots 10 are machined into the main body 1 through the upset central portion to accommodate fluid and cutting debris bypass. Now referring to FIG. 6, the progressive angled section 5,6,7 and 8 terminates just before the major diameter crown length with chamfered section 5 that has a series of pockets formed to accommodate diamond impregnated carbide inserts of the saddle style type 12 or of the semi domed type 14 in order to protect the transition from the aggressive diamond cutting structure to the non-aggressive carbide plaquet hard faced crown length or stabiliser section of the tool. Referring to FIG. 7 this can be more clearly seen with inserts 12 set into these pockets. The hard faced stabilised section of the crown length on the major diameter can also be seen with the carbide plaquets 15 evenly distributed and held in place by metal carbide powder 16. This crown length section being a ground finish to 0.020″ to 0.030″ below borehole diameter as is normally the case for conventional drill string stabilisers.

It will be appreciated that in other embodiments (not shown), the stabilising portion comprises pockets for receiving inserts. For example, the stabilising portion comprises an array of pockets for receiving stabilising diamond inserts. The stabilising diamond inserts comprise flat or flattened diamond inserts, such as to provide flat, non-aggressive bearing surface/s. The stabilising diamond inserts are ground or configured to define the maximum outer diameter or gauge of the stabilising portion. The stabilising diamond inserts are ground or configured after insertion in the pockets to define the maximum outer diameter or gauge of the stabilising portion. The stabilising diamond inserts are configured to only project minimally from the pockets. For example, the stabilising diamond inserts are configured to project no more than 3 mm, 2 mm or 1 mm from the pockets.

Now referring to FIG. 8 which shows a conventional stabiliser 21 in a borehole 19 drilled though relatively soft formation containing chert nodules 18 which have caused borehole deflections 20 and protrusions or ledges 23 projecting into the borehole. It can be seen that if the rotating drill string and conventional stabiliser 21 progresses to the next protrusion or ledge 23 that the unprotected angular lead up or leading edge 22 will be vulnerable to damage as it rotates into the protrusion or ledge 23. This is the normal mode of failure for conventional stabilisers in this environment.

Now referring to FIG. 9 which shows a hybrid stabilised diamond drilling reamer tool 24 in a borehole 19 drilled though relatively soft formation containing chert nodules 18 which have projected into the borehole path to potentially cause protrusions or ledges the first having been reamed away and the second to be reamed by the diamond. The diamond impregnated carbide inserts 12 and 13 mounted on the shallow sloping leading edge of the hybrid stabilised diamond drilling reamer tool between the upper and lower diameters 2 and 2 a and the major diameter hard face crown length section.

Now referring to FIG. 10 which shows a close coupled diamond reamer tool 7 with threadable means 3 and 4 at either end and similar diamond impregnated carbide insert cutting structure 12 and 13 mounted onto a shallow taper between the drill string diameter and the borehole diameter connected to a conventional shortened drill string stabiliser with non-aggressive hard facing along its crown length. It is recognized that the inventive aspect of this invention is the close coupling of an aggressive and progressive diamond reaming structure in very close proximity to a non-aggressive stabiliser structure and this can be achieved in a number of ways. As an integral structure as described in the preferred embodiment FIG. 1 to FIG. 5 or in a close coupled arrangement as shown in FIG. 10 which could be in the form of separate tools or in a piggy back or sleeve type arrangement. It will be appreciated that FIG. 10 shows only half of the arrangement, with a mirror-image replicated to the right hand side of the figure. Another half of the stabiliser is mirrored, together with a mirror image reaming portion or sub. Accordingly the arrangement of FIG. 10 allows stabilised reaming or reamed stabilisation in both uphole and downhole directions, with a leading portion of lesser diameter always comprising a reaming portion for initial contact of inclusions at a diameter less than the stabilising diameter of the major crown diameter.

In all cases the close coupling of stabilising and reaming capability in one tool or short assembly provides a system which can substantially improve drilling performance and stabiliser life in difficult formations containing large medium to large mass hard rock objects in otherwise relatively soft formation.

It will be apparent to those of skill in the art that the above described embodiments are merely exemplary of the present invention, and that various modifications and improvements may be made thereto, without departing from the scope of the invention. For example, where a drill string has been illustrated, other downhole tools or strings may be used in other embodiments.

It will be appreciated that any of the aforementioned tools may have other functions in addition to the mentioned functions, and that these functions may be performed by the same tool.

Where features have been described as downhole or uphole; or proximal or distal with respect to each other, the skilled person will appreciate that such expressions may be interchanged where appropriate. For example, the skilled person will appreciate that where the apparatus or string may move downhole in the embodiments shown; in additional or alternative embodiments or operations, the apparatus or string may move uphole.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention. 

What is claimed is:
 1. A method of stabilising at least a portion of a downhole toolstring, whilst the portion of downhole toolstring is in a soft formation with hard inclusions, the method comprising reaming the hard inclusions of said soft formation with a reaming portion of a downhole apparatus whilst stabilising the reaming portion of said downhole apparatus with a stabilising portion of the downhole apparatus.
 2. (canceled)
 3. (canceled)
 4. The method of claim 1, wherein the method comprises reaming hard inclusions projecting into the borehole or into the intended path of the borehole.
 5. The method of claim 1, comprising substantially only reaming the hard inclusions in the soft formation and substantially not reaming the soft formation.
 6. The method of claim 1, comprising stabilising the portion of toolstring against a bore wall of the soft formation.
 7. (canceled)
 8. The method of claim 1, wherein the method comprises at least one of stabilising and/or reaming at or to a gauge or diameter substantially similar to and just less than the gauge of pre-drilled borehole.
 9. The method of claim 8, wherein the method comprises stabilising with a stabilising portion with a major crown length diameter of 0.020″ to 0.030″ below borehole diameter.
 10. (canceled)
 11. (canceled)
 12. The method of claim 1, comprising reaming from a lesser outer reaming diameter which corresponds to a lesser outer diameter of the toolstring up to a maximum outer reaming diameter using an angled reaming portion extending axially backwards and radially outwards along a leading axial portion of an upset portion of the downhole apparatus, the maximum outer reaming diameter being less than a full gauge diameter of the borehole.
 13. The method of claim 1, comprising initially reaming with a part or surface of the reaming portion at or close to the diameter of the toolstring whilst the reaming portion is supported proximal the reaming portion by the stabilising portion proximal the reaming portion.
 14. The method of claim 1, comprising stabilising the portion of toolstring directly behind the reaming portion of the downhole appartus; and stabilising the toolstring adjacent the reaming portion of the downhole apparatus with a non-aggressive bearing outer surface of the stabilising portion of larger diameter than the reaming portion such that the reaming portion is substantially prevented from deviating or deflecting from a path aligned with the borehole.
 15. The method of claim 1, comprising reaming with a reaming portion of lesser diameter in advance of stabilising with a stabilising portion of greater diameter.
 16. A downhole apparatus for stabilising at least a portion of downhole toolstring in a borehole, the downhole apparatus being configured to stabilise the portion of the downhole toolstring whilst the downhole apparatus is in a soft formation with hard inclusions, the downhole apparatus comprises comprising: a reaming portion for reaming the hard inclusions; and a stabilising portion for stabilising the reaming portion whilst reaming.
 17. The downhole apparatus of claim 16, wherein the downhole apparatus comprises a fixed diameter or fixed gauge apparatus.
 18. (canceled)
 19. The downhole apparatus of claim 16, wherein the downhole apparatus comprises an upset portion extending radially from a lesser outer diameter of the downhole apparatus to a maximum outer diameter of the downhole apparatus.
 20. The downhole apparatus of claim 19, wherein the upset portion comprises at least one of the reaming portion and the stabilising portion.
 21. (canceled)
 22. (canceled)
 23. The downhole apparatus of claim 20, comprising a plurality of the upset portions, wherein the plurality of upset portions are closely coupled.
 24. The downhole apparatus of claim 19, wherein the upset portion is configured to stabilise at and/or ream to a gauge or diameter substantially similar to and just less than the gauge of pre-drilled borehole.
 25. The downhole apparatus of claim 24, wherein the stabilising portion comprises a maximum diameter 0.020″ to 0.030″ below borehole diameter.
 26. The downhole apparatus of claim 19, wherein the reaming portion is provided along an axial length of the downhole apparatus, the axial length extending in an axial direction of the borehole, and wherein the reaming portion comprises an aggressive surface and is provided on a progressive angled section of the upset portion, extending rearwards and outwards from a leading or front section of the upset portion.
 27. The downhole apparatus of claim 16, wherein the reaming portion of the downhole apparatus comprises an array of pockets formed to accommodate reaming inserts.
 28. The downhole apparatus of claim 16, wherein the stabilising portion of the downhole apparatus comprises a non-aggressive surface.
 29. The downhole apparatus of claim 28, wherein the stabilising portion of the downhole apparatus comprises at least one of: carbide plaquet hard facing along the crown length of the stabilising portion; pockets for receiving stabilising diamond inserts; pockets for receiving stabilising diamond inserts, the stabilising diamond inserts comprising flat or flattened diamond inserts ground or configured to define the maximum outer diameter or gauge of the stabilising portion.
 30. (canceled)
 31. (canceled)
 32. The downhole apparatus of claim 19, wherein the upset portion comprises a transition portion between the reaming portion and the stabilising portion, the transition portion configured to protect or shield the stabilising portion.
 33. The downhole apparatus of claim 19, wherein the stabilising portion of the downhole apparatus is disposed directly behind the reaming portion of the downhole apparatus, behind being taken in the direction of transit of the apparatus; and the reaming portion is of lesser diameter for reaming in advance of stabilising with a stabilising portion of greater diameter.
 34. (canceled)
 35. (canceled)
 36. (canceled)
 37. A toolstring comprising at least one downhole apparatus according to claim
 19. 38. (canceled)
 39. (canceled)
 40. (canceled) 